Yah, Lucas even talks about this in the audio commentary of the 2004 editions. He explains that the speed of a hyperdrive system is mostly determined by the strength of the navigation computer and not by it's engines. The better that computer is, the more precise it can calculate shortcuts that would represent a higher risk to ships who had a computer that couldn't deliver very precise course calculations in a short amount of time, and thus have to take a longer route to evade space hazards that could proove fatal to the ship and crew.